 "evaluates to 'true'."
                      (EMPTY-STRING))]
 
-    (let [pos   7] ; <== Can be set to either from 1 to infinity.
+    (let [pos   3] ; <== Can be set to either from 1 to infinity.
 ;   (let [subst "callable entity"]
 ;   (let [subst "AAA"]
 ;   (let [subst "+-="]

        (when (seq words)
            (let [word     (first words)]
            (let [word-len (count word )]
            (let [word-pos (if (< (- pos 1) word-len) (subs word pos)
                                                      (EMPTY-STRING))]

            (println (str (DBG-PREF) word))

            (if (= word (last words)) (throw (Exception.  (str text- word)))
                                      (recur (rest words) (str text- (cond
                (< (- pos 1) word-len)
                    (let [word- (str (subs word 0 (- pos 1)) subst
                                     (subs word      pos  ))]

                    (println (str (DBG-PREF) word-))

                    word-)
                :else (do
                    (println (str (DBG-PREF) word ))

                    word))
                (SPACE))))

; Helper constants.
(defmacro EMPTY-STRING []     "")
(defmacro SPACE        []    " ")
(defmacro COMMA        []    ",")
(defmacro POINT        []    ".")
(defmacro NEW-LINE     []   "\n")
(defmacro DBG-PREF     [] "==> ")
(defmacro SPACE-       []  #"\ ")
